The manufacture of .beta.-naphthol, according to the Hock process, necessitates .beta.-isopropylnaphthalene, which is subsequently oxidized to .alpha.-hydroxyperoxypropyl-2-naphthalene and treated with acid to undergo rearrangement-cleavage to give .beta.-naphthol and acetone.
Preparation of .beta.-isopropylnaphthalenes in solution is generally carried out by Friedel-Crafts type of alkylation processes using either Lewis acid halide catalysts, such as aluminum chloride, or over solid catalysts, such as supported phosphoric acid or aluminosilicates. All these reactions generally yield a mixture of .alpha.- and .beta.-isopropylnaphthalene, which subsequently needs to be separated and/or further isomerized. Further, aluminum chloride and the like Friedel-Crafts catalysts form highly colored complexes with the products, which must be decomposed upon work-up, resulting generally in loss of the catalyst and significant cost.
It was shown in studies of solution Friedel-Crafts isopropylation of naphthalene that mixtures of .alpha.- and .beta.-products are obtained (see "Friedel-Crafts and Related Reactions", ed. G. A. Olah, Vol. 11, Chapter XIV, Wiley-Interscience Publishers, New York, New York, 1964; H. E. Nursten and A. T. Peters, Journal of the Chemical Society (London) 129 (1950), G. A. Olah and J. A. Olah, Journal of the American Chemical Society 1976, 98, 1839.
Haworth, Letsky and Marvin, (Journal of Chemical Society, 1932, p. 1790) claimed to have obtained pure .beta.-isopropylnaphthalene by the reaction of isopropyl bromide with naphthalene in the presence of aluminum chloride, as did Price and Ciskowsky (Journal of the American Chemical Society, 60, 2499) in the reaction of 2-propanol and naphthalene using boron trifluoride as catalyst. U.S. Pat. No. 2,776,322 (W. Webster and D. Cheselden, 1957), however, demonstrated that these reactions, as well as related aluminum chloride catalyzed isopropylation with propene gave mixtures of .alpha.- and .beta.-isomers, which must be separated either by careful, very efficient fractional distillation or by crystallization.
Subsequently, the Friedel-Crafts alkylation of naphthalene with propene using H.sub.3 PO.sub.4.BF.sub.3 catalyst was reported to give 70% .alpha.- and 30% .beta.-isopropylnaphthalene (Friedman and Nelson, Journal of Organic Chemistry, 34, 3211 (1969). It was more recently shown in mechanistic studies with aluminum trichloride using dilute CS.sub.2 or CH.sub.3 NO.sub.2 solution with short reaction times and very low conversions that kinetic conditions tend to favor formation of the .alpha.-isomer, whereas thermodynamic conditions favor the .beta.-isomer. The thermodynamic equilibrium of the AlCl.sub.3 catalyzed solution isomerization of isopropylnaphthalenes was also established (Olah and Olah, Journal of the American Chemical Society, Vol. 98, 1839 (1976). However, so far no practical regioselective preparation of .beta.-isopropylnaphthalene has been achieved. U.S. Pat. No. 2,776,322, for example, clearly states that isopropylnaphthalenes obtained by Friedel-Crafts reactions are mixtures of the .alpha.- and .beta.-isomers, which need to be separated by highly efficient distillation or crystallization. U.S. Pat. No. 3,458,587 describes the catalytic liquid phase alkylation of naphthalene with propene over solid H.sub.3 PO.sub.4 to give mixtures of .alpha.- and .beta.-isopropylnaphthalenes which subsequently in a separate operation are isomerized by anhydrous hydrogen fluoride to give a higher ratio of the needed .beta.-isomer. U.S. Pat. No. 3,504,045 also teaches that Friedel-Crafts alkylation of naphthalene gives a mixture of the .alpha.- and .beta.-isomers. The content of the .beta.-isomer is increased by treatment of the alkylate with H.sub.3 PO.sub.4 over a solid support at elevated temperature. The product distribution at 350.degree. C. was 13% .alpha.- and 52.5% .beta.-iospropylnaphthalene, together with 16% naphthalene and 18% higher molecular weight polymeric products. U.S. Pat. No. 3,504,046 teaches alkylation of naphthalene over similar H.sub.3 PO.sub.4 catalyst on solid support. At 350.degree. C. at 800 psig propene, a product mixture consisting 16% naphthalene, 17% .alpha.- and 34.8% .beta.-isopropylnaphthalene was obtained.
The prior art of the alkylation of naphthalene is summarized in recent U.S. Pat. No. 4,026,959 (1977) describing an isomerization process for isopropylnaphthalenes. It states, "Thus, there is no method of which we are aware to efficiently produce isopropylnaphthalene in high yield and high beta isomer content and with economic use of catalyst by direct alkylation of naphthalene with propylene. This is true regardless of the catalyst used as far as we are aware. There remains, therefore, a need for an economic process for the preparation of beta-isopropylnaphthalene in high yield and high purity, from naphthalene and propene" (as well as other alkylating agents). The present invention discloses such a method.